European fertility rates have been below the replacement rate of 2.1 children born per woman for decades. The U.K. and France have hovered near the replacement rate for most of this period, but birth rates in Germany, Spain and Italy have been limping along at crisis levels since the 1980s.

Think of it this way: Here in the United States, we hear about the next great generation — the millennials (also called Gen Y and echo boomers) — and how they will shape the country in the decades ahead. Numerically and culturally, they are the most important generation since the postwar baby boomers.

Well … let’s just say that no such sentiment exists in Germany, Italy or Spain. None of these countries had a secondary baby boom in the 1980s and 1990s. The young personalities dominating the discussion here were simply never born in Europe.

Of course, young workers that were never born will not be able to pay taxes or man the factories of tomorrow. This is the point that Gillian Tett makes, and it is a valid one.

But it also happens to miss the very large elephant in the room: Workers can be replaced by automation and outsourcing; consumers cannot.

To carry this a step further, General Motors (GM) or Ford (F) can program a robot to build a car. But that robot has no interest in buying a car. And as roughly 70% of the modern economy is consumer spending, that’s a big problem. Without a steadily growing population, the modern consumer economy breaks down.

I’m picking on Tett; she has a much better grasp of the importance of demographics than most journalists, and she clearly has done her homework. But virtually everyone in the economics and investment professions that follows demographics (yes, there are a surprising number of us) focus their energies in the wrong places. They focus almost solely on supply. Demand — when it is considered at all — is viewed as a byproduct; something that just happens on its own. (For the geeks in the room, this concept has a name: Say’s Law.)